Gustav Set to Engulf Louisiana

Hurricane warnings are in place, evacuations have been ordered, and we are left to watch as Hurricane Gustav bears down on the coast of central and southeast Louisiana. Already, some of Gustav's outer rain bands are coming ashore. If there's any good news, Gustav weakened as it traversed western Cuba and has not re-intensified over the Gulf of Mexico. As of 5 p.m., it had maximum winds of 115 mph making it a Category 3 storm. Will Gustav strengthen or weaken before hitting land? The National Hurricane Center says:

THE EYE HAS MOVED NORTHWEST OF THE DEEP WARM WATER OF THE LOOP CURRENT...AND THAT COMBINED WITH THE LIKELIHOOD OF CONTINUED SHEAR REDUCES THE CHANCES OF SIGNIFICANT INTENSIFICATION.

Keep reading for more Gustav and a short update on Hanna. For Washington, D.C. weather, see our full forecast.

Overall, the upper level wind environment is favorable for intensification, but not as favorable as during yesterday's rapid intensification. Gustav is currently over the Loop Current, containing the highest heat content waters of the Atlantic.

But he also suggests the window for strengthening may soon close:

By this evening, Gustav will be passing over a cold eddy. The heat content of the Gulf will decrease as Gustav approaches the coast.

Another factor which may weaken Gustav as it nears land is entrainment of dry air. Considering the various factors for strengthening and weakening together, the National Weather Service's official intensity forecast brings Gustav ashore as a low-end Category 4 Category 3 hurricane with winds to 130-135 mph 125 mph (updated at 5 p.m.).

While storm intensity will play a major role in the severity of Gustav's impacts, the extent of its impacts will greatly depend on exactly where it strikes land. On Friday, I mentioned the worst case scenario would be landfall just to the west of New Orleans where "just to the west" means within about 50 miles. A landfall further west than that would place New Orleans outside the quadrant of the storm with the strongest winds and highest storm surge.

Fortunately, most track models currently bring Gustav ashore slightly west of the worst case track, but it's so close that New Orleans will still likely experience a serious storm surge and even a devastating storm surge with just a modest shift to the east. The SciGuy at the Houston Chronicle takes an in-depth look at this unwelcome possibility and concludes:

In such a scenario water would flood into the city from the lake, which could drown the city again, and possibly to an even worse degree [than Katrina].

On a positive note, the storm's weakening over the Cuba, has reduced the likelihood of a catastrophic surge in New Orleans. Jeff Masters explains:

The extent of Gustav's current weakening was unexpected, and this could substantially reduce the storm surge. Given the current intensity forecasts, I believe there is a 60% chance that a lower storm surge of 12-15 feet, characteristic of a Category 3 hurricane, will affect the city. If the Army Corps of Engineers' assertion that the levee system can withstand a Category 3 hurricane is correct, the levees will hold.

If the potential for a 12-15 foot storm surge wasn't bad enough, New Orleans and much of Louisiana will likely receive copious amount of rain. NOAA's Hydrometeorological Prediction Center predicts 10-15" of rainfall for most of the state.

Gustav is forecast to officially make landfall at 7 a.m. Monday morning -- which is about the same time Katrina made landfall on a Monday three years ago. Want a sense of what New Orleans is about to face?:

This Afternoon: Scattered showers and thunderstorms. Mostly cloudy, with a high near 89. East wind around 15 mph. Chance of precipitation is 50%.

Tonight: Tropical storm conditions expected, with hurricane conditions possible. Scattered showers and thunderstorms, then showers likely and possibly a thunderstorm after 1am. Some of the storms could produce gusty winds and heavy rain. Mostly cloudy, with a low around 78. Northeast wind 20 to 25 mph increasing to between 30 and 40 mph. Chance of precipitation is 70%.

Labor Day: Hurricane conditions expected. Showers and possibly a thunderstorm. Some of the storms could produce gusty winds and heavy rain. High near 82. East wind 50 to 60 mph increasing to between 50 and 70 mph. Winds could gust as high as 85 mph. Chance of precipitation is 100%.

Monday Night: Hurricane conditions expected. Showers and possibly a thunderstorm. Some of the storms could produce gusty winds and heavy rain. Low around 80. South wind 40 to 60 mph decreasing to between 25 and 30 mph. Winds could gust as high as 75 mph. Chance of precipitation is 100%.

Tuesday: Tropical storm conditions possible. Showers and possibly a thunderstorm. Some of the storms could produce gusty winds and heavy rain. High near 83. Chance of precipitation is 90%.

Even after Gustav departs, it will take a long while for New Orleans to dry out, as showers and thunderstorms remain in the forecast through the weekend.

There is another storm out there which continues to bear watching: Tropical Storm Hanna. It hasn't strengthened over the last several days, and its intensity forecast remains "problematic" according to the National Hurricane Center, especially in the short term. The long-term forecast does indicate some intensification and track forecasts bring Hanna towards the southeast U.S. coast late next week, although there is some variability. We'll keep you posted on this storm.

Your article neglected to mention that www.weatherbug.com is also a valuable resource for coverage on Gustav and Hanna. You can track the storm, watch animated satelite images and link to more than 1,500 weather stations and cameras located across the entire Gulf Coast.

by the looks of the satellite loop, Gustav seems to be headed directly for the New Orleans area. hopefully it does veer off to the west just slightly as predicted and also lets hope that Gustav doesn't pull a Charlie and strengthen as he comes ashore.

I've followed the 12Z and the 18Z GFS and I predict Hanna to make landfall on the Grand Strand, SC. The 18Z is rarely identical to the 12Z GFS and in this case, it is, which means the GFS has latched on to something the other models are not picking up on yet. Usually when the GFS puts a stake in the ground, the other models come around (Fay is a case in point). If Hanna makes landfall on the Grand Strand, Washington DC is in trouble, because she won't waste time moving northward.

Gustav--I watched the latest GOES IR Floater loop twice and I suspect the eye may reform about 50 miles south of where it is now in the deepest convection. If that occurs, I predict Gustav will make landfall as a Cat 4.

I'm going to go with a Cat 2, maybe 95-100 at landfall. I'd be very suprised if we get any verified sustained winds over hurricane force. It's a good thing it peaked so early. Looks like it's much less of a grave situation than what could have happened.

Check out the latest GOES loop. I see an eye and a CDO forming again around the eye, not just in the SW quadrant. Gustav is definitely intensifying and appears to be doing so rapidly. Right now the eye appears to be located at 27.0N,-87.8W.

No doubt that the storm is up to something that the NHC did not predict in their 5pm update. While earlier today I was almost certain that this storm was looking to fizzle - tonight it is winding up into a tight ball of power and I would not be shocked to now see it as a Cat 4! The damage is going to be tremendous and we might as well say goodbye to New Orleans as we have known and loved it in our lifetime. It just does not make sense to build and maintain a city in a bowl.

Steve and Greg- I'm not seeing a well defined eye in satellite loops, although radar is a different story. With the storm's recent better organization however, I would not be surprised to see one in a little while.

Hey folks, I'm looking at IR satellite images and stuff, but none of them come with some sort of key for people who don't already know how to read them. I don't know what all of those colors mean and the scale just has numbers that mean nothing to me. Can anybody give me a brief tutorial on how to look at IR satellite or post a link to a website that can?

Laura: Follow this link-http://www.ssd.noaa.gov/goes/flt/t1/loop-avn.html
which brings you to an IR loop for Gustav. Once the images load, click the checkbox next to "IR Temp". On the bottom, you will see "DEG C" and numbers corresponding to colors. These indicate the temperature of cloud tops. The colder the cloud tops, generally, the higher the cloud, and the stronger the convection in the storm.